1. Field of the Invention
The present invention generally relates to a developing device for use in an electrophotographic copying machine, a printer or the like and more particularly, to a developing device which visualizes an electrostatic latent image formed on a photoreceptor by supplying monocomponent developer.
2. Description of the Related Art
Japanese Patent Laid-open Application No. 52-143831 discloses one such monocomponent developing device, in which a blade presses a supply of non-magnetic toner against the surface of an elastic developing roller so that a thin layer of charged toner may be formed on the peripheral surface of the developing roller. A toner image is then, formed by bringing this layer of charged toner into direct contact with the surface of the photoreceptor.
Alternatively, Japanese Patent Laid-open Application No. 61-176959 discloses another monocomponent developing device, in which the photoreceptor is pressed against the a developing roller. The developing roller of this device is a soft, foamed elastic member which, for example, sponge rubber, urethane rubber, or the like for the purpose of expanding the contacting (developing area) between the developing roller and the photoreceptor as well as improving the efficiency of the developing process.
Both of these methods require a blade to press the surface of the developing roller with enough pressure to form an even toner coating. Consequently, the developing roller needs to be relatively hard in order to resist the pressure of the blade. But on the other hand, to prevent damage to the photoreceptor or smearing of the image formed between the developing roller and the photoreceptor, the developing roller needs to softly contact the photoreceptor. These contradictory requirements for a hard and soft developing roller are one impetus behind the present invention. Another motivating factor is the reduced clarity of the image formed on the photoreceptor when the peripheral speed of the developing roller is different from that of the photoreceptor.